1. Field of the Invention
The present invention relates to a valve for an anti-lock brake system. More particularly, the present invention relates to a valve for an anti-lock brake system, in which a sleeve sheet is assembled with a lower portion of a valve housing, so that the external shape and the structure of the valve are simplified.
2. Description of the Related Art
In a hydraulic brake system of a vehicle, hydraulic pressure is applied to a master cylinder according to an operation of a brake pedal, so that braking is achieved. At this time, if braking force is greater than static friction force between a tire and a road, the tire may slip on the road, which is called “slip phenomenon”.
However, since a dynamic coefficient of friction is smaller than a static coefficient of friction, the slip phenomenon must be prevented to realize an optimum braking operation. In addition, handle-lock phenomenon that makes it impossible to control a handle during the braking operation must be prevented.
For this reason, there has been suggested an ABS (anti-lock brake system) which prevents the handle-lock phenomenon by controlling hydraulic pressure applied to a master cylinder. The ABS basically includes a plurality of solenoid valves, an ECU for controlling the solenoid valves, an accumulator, and a hydraulic pump.
The solenoid valves are classified into normal-open type solenoid valves, which are installed at an upstream side of a hydraulic brake and normally maintain an open state, and normal-close type solenoid valves, which are installed at a downstream side of the hydraulic brake and normally maintain a closed state.
Referring to FIG. 1, a conventional normal-close type solenoid valve (hereinafter, simply referred to as a solenoid valve) is installed in a modulator block 1 to increase the integration degree. A valve bore 2 is formed in the modulator block 1 through a cutting process such that a valve can be installed in the valve bore 2.
The valve bore 2 is communicated with an internal fluid path formed in the modulator block 1 and a valve housing 3 is inserted into the valve bore 2.
A cylindrical sleeve 5 is coupled to one end of the valve housing 3 such that an armature 4 installed in a hollow section of the valve housing 3 can move up and down through the cylindrical sleeve 5, and a valve core 6 is coupled to an open end of the sleeve 6 to close the open part of the sleeve 6 and to allow the armature 4 to move up and down.
In addition, the armature 4 is provided at an end portion thereof with a plunger 8. The plunger 8 opens/closes an orifice 7a of a valve seat 7 as the armature 4 moves up and down, and extends toward the valve seat 7 installed in the hollow section of the valve housing 3.
A spring 9 is installed between the armature 4 and the valve core 6. The spring 9 elastically supports the armature 4 such that the orifice 7a can be maintained in a closed state by the armature 4 in normal time. An excitation coil (not shown) is provided at an outer portion of the sleeve 5 and the valve core 6 in order to induce electronic interaction to move the armature 4 up and down.
As power is applied to the excitation coil, electromagnetic force is generated between the valve core 6 and the armature 4, and the armature 4 is moved toward the valve core 6 due to the electromagnetic force, thereby opening the orifice 7a of the valve seat 7. In contrast, if the power being applied to the excitation coil is shut off, the electromagnetic force is not applied to the armature 4, so the armature 4 returns to its original position by elastic force of the spring 9. Thus, the orifice 7a is closed.
However, according to the conventional solenoid valve having the above structure, components are installed about the valve housing 3, so the valve housing 3 must be formed with a space for installing the plunger 8, the orifice 7a, the valve seat 7 and a sealing member 10. In addition, the valve housing 3 must be formed with an inlet 3a and an outlet 3b for fluid communication. For this reason, the valve housing 3 may have a complicated configuration, so that the valve housing 3 must be processed through a plasticizing process, such as a forging process, and a precise cutting process. Therefore, the size of the valve housing 3 is enlarged, so that the size of the solenoid valve is also enlarged, causing increase in the manufacturing cost for the solenoid valve.